1. FIELD OF THE INVENTION
The present invention refers to a continuous freeze drying apparatus that can be employed in a particularly advantageous way when the treatment of great amounts of the same product is required.
2. BACKGROUND INFORMATION
As well known, freeze drying or lyophilization is a physical treatment to which perishable organic substances are subjected in order to ensure their long preservation.
It consists of a drying or dehydration process carried out under low temperature and vacuum conditions, where a diluent, usually water, is removed from the desired product through direct evaporation from the solid state (drying by sublimation).
U.S. Pat. No. 4,590,684 in the name of EDEN RESEARCH LABORATORIES, INC. describes a continuous freeze drying apparatus containing an inlet and a passageway for slurry material, an underlying holed plate including cooling passageways whose double function is cooling the plate and freezing the slurry passing through it, and a sublimation passageway that crosses the plate on the opposite surface to the inlet side.
A reduced pressure is kept inside the sublimation passageway and the pressure drop is kept within the plate area containing the slurry.
Next to the above-mentioned plate, in the sublimation passageway, a heating element checks the movement of the slurry cooled through the passageway increasing its sublimation upon entry.
This apparatus, however, has the disadvantage of providing a freeze dried product that is dimensionally dishomogeneous and morphologically uncontrolled, further requiring a subsequent intervention to make it powdery or granulated.
U.S. Pat. No. 3,740,860 in the name of SMITHERM INDUSTRIES, INC. describes a continuous freeze drying apparatus where a product is freezed onto a conveyor in a freezing compartment inside a vacuum vessel in which the pressure is high enough to keep volatiles from evolving from the freeze dried product.
This apparatus is provided for a continuous supply with a good amount, thus generating a compact output material and not a granulated one that can be more easily controlled and treated.